Protection History

Authors: Walter Schossig, Germany, and Thomas Schossig, OMICRON electronics GmbH, Austria

Relay Testing - Test Sets and testing Technology in the 1960s

In 1960, the IEC's TC 41 "Electrical relays" was founded and the first German autonomous standard for relays, the VDE 0435/9.62 "Standards for relays in high current systems" was released in 1962. International and national committees published requirements that have become mandatory for the producers and users of protection relays. This also has effects on technology used for testing and on the properties of test sets. The multitude of relays built into a generator's protection cubicle lead to the solution of one built-in test set per generator.
The test set for machine protection developed by Siemens-Schuckertwerke (SSW) in the 1950s, RG491, was further developed into the RG493 in 1964. It consists of a relay combination in a sheet-steel enclosure and accessories (see Table 1). For the creation of test currents, an auxiliary alternating voltage from a transformer under test (75/24V) connected to a voltage transformer or the measuring winding of a grounding transformer was used. The connection symbol was chosen so the test current is approximately equal to the load current (the maximum deviancy is 13,4% with cos phi = 0,5 to 1).

The auxiliary alternating voltage serves to supply the relays in the test set and is created using a three-phase bridge connection without a smoothing capacitor.
This way, the test set can immediately close the tripping channels if a problem occurs during testing and the voltage between the phases drops down. Figure 2 shows the connection scheme of RG491 and Figure 5 the solution for stator fault protection in RG493.
BBC developed a "Half-Period Distance Relay" for the high voltage in 1964 (Figure 4).
It came with a built-in test set and an autorecloser.

Also, the electronic busbar protection (1966) was equipped with testing possibility (Figure 1). The example shows double busbar with auxiliary busbar, coupling and 25 feeders.
The test could be started manually or automatically via the clock built in. The testing took just 2..3 seconds
The English Electric Company (EE) released in 1967 the overcurrent relay portable test equipment CFB (Figure 3) and the Distance relay portable test equipment ZFB (Figure 6 and Figure 7).
Depending on the developments in protection, the vendors produced test equipment making testing possible.

AEG's RED1 (Figure 8, Figure 9, and Figure 10) was famous at this time. High accuracy and simple measurement methods made the application easy. It could be used as long as pure impedance characteristics without under-impedance startup were used.

In the 1960s angle dependent characteristics became possible, as well as underimpedance startup. Since the number of relays used also increased dramatically, a new test set was required. The device 65a and 65b (Figure 11) made it possible to test such devices without auxiliary devices. There was a variant consisting of two parts delivering testing current and testing voltage, so overcurrent, voltage relays, time relays and directional relays could be tested.  Even the fast distance relays SD4 and SD14.
The third device made phase shifts possible and extended the testing range.
The devices were portable and came with a lid made of steel.
Connecting leads were used. The devices could be locked and came with a handle. Table 2 summarizes the dimensions. The test was powered by 110 V, and for the application in 220 V grids an auxiliary transformer was used. To test ellipse characteristics with different angles an auxiliary coil was necessary (Figure 11).

ZERA extended its product portfolio in 1963 with two portable testing devices- controller and high current device RRa5 and RRa7,5 (Figure 12 and Table 3).  The powerful devices have been used for primary tripping devices as well as relays. Wheels allowed transport, as well as handles. The covers are isolated, white letterings make connections easy.
In the 1960s ZERA produced several load transformers. Those devices could be used for billing meters testing as well as for measurement transformers. Additionally, primary and secondary testing of protection was possible.
See Figure 13 and Figure 14 for details as well as Table 4.

EAW in Eastern Germany launches the relay test set PE1 (Figure 15 and the Figures on page 70).
This single-phase device was developed for distance relays including autorecloser. But also, other line protection relays such as overcurrent relays, direction relays, earth fault and earth fault detection and voltage relays could be tested. All elements have been mounted on a hard board. The operating knobs (2) and switches (11) have been mounted in that manner, that easy operation with the right hand was possible. On the underside stands could be mounted.

The clock included could be stored safely for transport. The lid protected the operating elements.
To measure impedances, it had to be independent of voltage variations. To do so the voltage drop created by the current flowing in the line impedance replica was used.
The line impedance replica consisted of resistance and coils. The typical line angles (0°, 60°, 70° and 80°) could be set up simply. The impedances had to be chosen in steps related to 10 A. An additional switch allowed impedance variation ±5%. The current outputs have been fixed (Table 5).  Remote control was possible via cables (on and off).

ASEA developed in 1966 TURE for overcurrent and voltage relays. (Figure 16 and Table 6).
In 1967 ASEA launched the test set TURG100 (Figure 17 and Table 7). The set comprises of two parts: The regulating unit and the high current supply unit.
It consists of a regulating unit, auto transformer with different tappings to connect to the different supply voltages and a sliding transformer for continuously regulating the test current.
The high current transformer made 1000 A injections possible. Connecting cables and clamps have been delivered.

Another combination of 30 A secondary and 1000 A primary testing was a device produced by Associated Electrical Industries Ltd., Manchester (A.E.I.) in 1968 (Figure 18 and Figure 19/ Figure 20).
This device allowed functional and tripping tests.     


Walter Schossig (VDE) was born in Arnsdorf (now Czech Republic) in 1941. He studied electrical engineering in Zittau (Germany), and joined a utility in the former Eastern Germany.  After the German reunion the utility was renamed as TEAG, Thueringer Energie AG in Erfurt. There he received his Master’s degree and worked as a protection engineer until his retirement. He was a member of many study groups and associations. He is an active member of the working group “Medium Voltage Relaying” at the German VDE. He is the author of several papers, guidelines and the book "Netzschutztechnik
[Power System Protection]". He works on a chronicle about the history of electricity supply, with emphasis on protection and control.

Thomas Schossig (IEEE) received his master’s degree in Electrical Engineering at the Technical University of Ilmenau (Germany) in 1998. He worked as a project engineer for control systems and as a team leader for protective relaying at VA TECH SAT in Germany from 1998 until 2005.
In 2006 he joined OMICRON as a product manager for substation communication products. He is author of several papers and a member of standardization WGs.